When an SMTP session starts, xf-spf is expected to be forked from
qmail-smtpd - this is why you need SMTPEXTFORK. When forked, this processes
gets all enviroment variables which were available for the parent process
(qmail-smtpd).
PR: ports/116332
Submitted by: Felippe de Meirelles Motta <lippe@freebsdbrasil.com.br>
Approved by: stas (mentor)